Citing current and former U.S. national-security officials, the report says Chinese and Russian secret agents are believed to be to blame. It’s alleged they were on a on a mission to navigate the U.S. electrical system and its controls.

The article says the intruders haven't sought to disrupt the power grid, but during a crisis or war, they could try to do so, resulting in a huge blackout.

Protecting the electrical grid is a key part of the Obama administration's cybersecurity review, which is supposed to come out next week. The daily – referring to "people familiar with the budget" – writes that under the George W. Bush administration, Congress approved $17 billion (US) in secret funds to protect government networks.

The new administration is considering whether to expand this program when it comes to private computer networks.

U.S. Department of Homeland Security Secretary Janet Napolitano told reporters that the power grid was vulnerable to potentially disabling computer attacks. However, she refused to comment on whether or not an intrusion had taken place.

Meanwhile, it’s not the first time the U.S. has suspected the Chinese and Russians of attacking it in cyber space.

An official speaking anonymously to Reuters said it’s the Chinese who have been really active lately. The source is quoted as saying:

"They are all over the place…They're getting into university systems, contractor systems, hacking government systems. There's no reason to think that the electrical system would be immune."

But many doubt it’s likely that China would want to disrupt the US electrical system since the Asian country holds the majority of American government debt, and relies on US consumers for much of its business.

As for Russia, it looks as though any time the U.S. speaks of espionage, Moscow comes into the spotlight.

The Journal writes that Russian and Chinese officials have denied any wrongdoing. It quotes Yevgeniy Khorishko, a spokesman at the Russian Embassy, as saying: "These are pure speculations. Russia has nothing to do with the cyberattacks on the U.S. infrastructure, or on any infrastructure in any other country in the world."